Right at this moment I'm working on studying Titan's atmosphere
and surface using near-infrared spectroscopy. A very general description
of this topic is below, including some of the most recent results
from throughout the community. For more details, please take a look at the
publications that I have contributed to. Soon I'll be posting
some of the IDL routines I've written in the course of my research, so please check back
for that, and feel free to contact me if you have any questions or comments.

The image of Saturn (above) was acquired using the guider
camera on the Shane
3-meter telescope at
Lick Observatory. The camera is imaging the light that is reflected off of
a shiny metal plate with a rectangular opening, or aperture, that leads into the
Hamilton Spectrometer. At the time we were using
the aperture that's near Tethys in the image. Although we were taking spectra
of Titan, which was out of the guider camera's field of view, roughly where the
spinning animation is.

The animation of Titan (top right) was created using a surface albedo map of
Titan that was assembled together by the Cassini
Imaging Team. This type of reprojection is useful for comparing ground-based
observations. For an brief description of Titan with beautiful pictures, please
check the
wikipedia.

Titan's has many diverse geological features, which suggest that
(much like Earth) there are a range of surface interactions with the subsurface
and the atmosphere. One slight complication in studying the surface is that to
see it, we have to take pictures with infra-red cameras. Using IR wavelengths
is not too much of a problem as far as analyzing
images of structures that we clearly resolve:
pebbles and rocks, hills and valleys, places where fluid
(probably liquid methane) once flowed, and lakes
(no lakes have been confirmed, but
this thing
looks suspicious) are all relatively
easy to interpret. However, there is a bit of a problem in deciphering the images of
features that we don't make out clearly (or resolve), like many of the structures seen
here in the animation at the top of the page.

To get a feel for the problem, first consider Earth.
We know immediately from looking at a satellite image of Earth that
the blue regions are water, the green and brown parts are land (plants, trees, dirt)
the white parts are snowy or cloudy. Try it: take a look at Google Earth and test
if you can stump yourself, start zoomed in (where it's easy) and then zoom out.
Better yet, start zoomed out, make a prediction, and zoom in to see if you were correct.
Taking another dimension of information besides just color, like brightness
(you intuitively do this looking at pictures), one could add a level of sophistication
to their interpretation. For example, smart people who study satellite photos of Earth
for a living [link] can tell you the difference between light brown
and dark brown, or light green and dark green [link]. Now think of a
black and white satellite photo (or look at these). Here the only information you have
is brightness, and sometimes it's easy to know what you're looking at, other times it's
trickier.

On Titan, we haven't yet developed the vocabulary to figure our how to translate
1-micron, 2-micron, and 5-micron into (for example) blue, green, and/or brown. We
also don't quite know what it means to be brighter or darker at any of these wavelengths.
This is one of things we're working on. We know that Titan is dark. At the infra-red
wavelengths that we use to see the surface, only about 5-20% of the light that reaches
the surface is reflected back. This is the same at most wavelengths, which means that
if we could combine Titan's infra-red wavelengths to make colors like our eyes do with
visible wavelengths, we would see that Titan isn't just dark, it's dark grey.
Mostly dark grey. Since there are these spots that jump out at you at 2- and 5-microns
(Barnes et al., 2005).
We've been using a Very Large Telescope (literally) to look at regions of Titan that have
been found to be particularly bright at 5-microns. Imagine walking along a dark-grey
landscape and seeing a big red thing in front of you -- that's what researchers using
Cassini saw [link]. They couldn't quite tell if the bright `red' (we don't really know if
5-micron translates to red) spot was on the ground, or in the air, but they thought it was
on the ground. Our measurements with telescopes further support the 'on the ground' idea,
but we're still working on understanding what the spot is.

The Enshrouding Haze of Aerosols

Smogs, fogs, caps, hoods, and collars. These are some of names for the aerosol particles
suspended in Titan atmosphere. Altogether they are called hazes, and the different names
are for regions (regions the size of continents) where there is more haze or less haze,
causing images of Titan, at certain wavelengths, to be brighter or darker.
That way it works is that all of the infra-red light that we see when observing Titan
is sunlight scattered by aerosols or reflected from the surface.
The size, structure, and chemical composition of a particular aerosol will each determine
how it scatters light. Any remote observations will measure scattering
from a large number particles with a distribution of sizes, structures, and
compositions --- each of which depend on the altitude and location of the
particular ensemble of particles being probed. On Titan, some
combination of these properties change with time and result in
seasonal changes in Titan's albedo. These changes in albedo are commonly interpreted as
changes in the aerosol density, primarily driven by circulation.

The stratospheric haze (left) is concentrated near the north
pole while the tropospheric haze (right) us concentrated near the south pole.

Using spectra from all infrared spectroscopy, we've been able to measure just how much
of an increase there is in both the stratospheric and tropospheric aerosols near the poles.
We have also measured how the aerosol extinction (the total amount of aerosol
scattering and absorption) changes with latitude. In the troposphere, there is a hood
around the South pole to 60 degrees South latitude where the aerosol extinction is
50% greater than near the equator and nearly constant. There is a decrease in aerosol
density from 60 to 40 degrees, marking the edge of the hood.
The stratosphere shows the opposite trend. We find that starting from right about
the Southern polar hood the stratospheric haze increases linearly towards the north pole
where there is 70% more haze than near the south pole.

These analysis of these data provides a new level of constraints of models of Titan's
atmospheric circulation, models that have until now only needed to reproduce
qualitative trends in aerosol extinction.
The Clouds

Titan is covered with clouds. A "zoo" of them, proclaims a
prominent editorial.
We don't have names for all the different clouds yet
(no `methano-nimbus' or `Titano-stratus'), but mechanisms for cloud
formation
have been proposed
based on how quickly they form and change with altitude.
Microphysical models of the clouds? It's true!
French researchers describe
many of the observable characteristics of Titan's clouds (e.g., where and how often
they form, how long they persist) using the same physical models as for cloud
formation on Earth. This is particularly interesting because it has been suggested
that Titan is a model of was Earth used to be like, and it has been a surprise
to everyone to learn just how similar the atmospheric and geological processes on
Titan are to those on Earth right now.